The invention relates to a fuel injection valve for internal combustion engines, such as is used for the injection of fuel into combustion chambers of fast-running auto-ignition internal combustion engines.
Fuel injection valves, such as are suitable for injecting fuel at high pressure into combustion chambers of internal combustion engines, are known for example from DE 10 2008 001 330 A1. Such fuel injection valves have a valve body in which there is arranged a longitudinally displaceable, piston-like valve needle. The compressed fuel, which is made available in a central high-pressure accumulator connected to the fuel injection valve, is introduced via multiple injection openings into a combustion chamber, wherein the nozzle needle opens and closes the injection openings. The longitudinal movement of the nozzle needle is controlled by way of the fuel pressure in a control chamber. The control chamber acts on that end of the nozzle needle which is averted from the valve seat, such that a closing force is exerted on the nozzle needle by the fuel pressure in the control chamber. By way of a control valve, the fuel pressure in the control chamber can be adjusted, such that the nozzle needle moves in a longitudinal direction in accordance with said pressure.
During the operation of the fuel injection valve, a high fuel pressure prevails at all times in the control chamber and also in the pressure chamber that surrounds the nozzle needle. When the internal combustion engine is shut down, however, said fuel pressure decreases to ambient pressure, such that the hydraulic closing force on the nozzle needle is eliminated, and the latter possibly opens in uncontrolled fashion. To prevent this, there is provided within the pressure chamber a closing spring which surrounds the nozzle needle and which, by way of its compressive preload, holds the nozzle needle in its closed position, even when the fuel pressure in the fuel injection valve has fallen to ambient pressure. In order that the closing spring can transmit the force optimally to the nozzle needle, there is formed on the outer side of the nozzle needle a shoulder against which a spring plate bears, with the closing spring resting in turn on said spring plate and thus exerting the closing force on the nozzle needle. The nozzle needle must therefore be equipped with a corresponding diameter step, which complicates the production process and thus increases production costs. Furthermore, the spring requires an adequate structural space in the pressure chamber, which limits a miniaturization of the fuel injection valve.